1. Field of the Invention
The present invention relates to a sheet stacking apparatus for stacking a sheet discharged from a sheet discharge port, and also relates to an image forming apparatus provided with the sheet stacking apparatus.
2. Description of the Related Art
Conventionally, an image forming apparatus thermally fixes a toner image formed on a sheet, discharges the sheet from a sheet discharge port, and stacks the sheet on a sheet stacking tray located outside the apparatus.
In recent years, the air conditioning at a work place or offices does not often rely on air conditioners alone, in view of energy saving and environmental issues. For example, windows are opened at offices and electric fans are used for the air circulation. Even in the winter season, electric fans are used together with a heating system. The electric fans cause the air to circulate in the offices in order to increase a heating efficiency.
In such environment, an image forming apparatus may be situated near the windows, and the electric fan may be put near the image forming apparatus. In this case, the wind from the open windows or the electric fan may disturb an arrangement of sheets on a sheet stacking tray, blow off the sheets, and cause the sheets to drop from the tray. If the wind blows against the sheets that are being discharged, the sheets are disturbed by the changing intensity of the wind, and the order of the sheets stacked may be different from the order of the sheets discharged. Then, the sheets are not stacked in the desired order of pages. In this manner, the wind blowing against the sheet stacking tray may deteriorate the sheet stacking performance. In particular, thin sheets are easy to fly with the wind, and the sheet stacking performance may significantly deteriorate.
In some countries, the image forming apparatus is installed outside the office building. In a certain country, for example, a street stall may have an image forming apparatus located inside the street stall. This is a copy-taking shop on the street. In such on-the-street copy-taking shop, the sheet(s) on the sheet stacking tray may fly with the wind, drop on the street, scatter, and become dirty.
In order to prevent the sheet(s) from falling off from the sheet stacking tray and scattering, Japanese Patent Laid-Open No. 7-315670, for example, proposed one technique.
According to the technique disclosed in Japanese Patent Laid-Open No. 7-315670, the sheet stacking tray is formed on the upper face of the apparatus main unit cover. A sheet pressing member is pivotably provided on the cover for pressing the stacked sheet(s) toward the sheet stacking tray so that the sheets stacked on the sheet stacking tray do not fall from the sheet stacking tray or scatter even when the apparatus main unit cover is opened.
With the technique disclosed in Japanese Patent Laid-Open No. 7-315670, it is possible to press those sheets which are already stacked on the sheet stacking tray by the sheet pressing member, but it is not possible to press those sheets which are being discharged. As such, when the wind blows against the sheets that are discharged toward the sheet stacking tray during the discharging process, the order of the sheets discharged may be different from the order of the sheets stacked on the tray, and the sheets are not stacked in the order of pages.